Memory device and reference circuit thereof

ABSTRACT

A device includes memory cells, a first reference switch, a second reference switch, a first reference storage unit, a second reference storage unit, and an average current circuit. The memory cells are each configured to store corresponding bit data. The first reference switch and the second reference switch are turned on when a word line is activated. The first reference storage unit generates a first signal having a first logic state when the first reference switch is turned on. The second reference storage unit generates a second signal having a second logic state when the second reference switch is turned on. The average current circuit averages the first signal and the second signal to generate a reference signal to be compared with a current indicating the bit data of one memory cell, in order to determine a logic state of the bit data of the memory cell.

RELATED APPLICATIONS

The present application is a continuation application of the U.S.application Ser. No. 15/667,600, now U.S. Pat. No. 10/157,654, filedAug. 2, 2017, which is a divisional application of the U.S. applicationSer. No. 14/929,076, now U.S. Pat. No. 9,754,639, filed Oct. 30, 2015,all of which are herein incorporated by reference.

BACKGROUND

Memory devices have been widely utilized in many applications. Invarious applications, the memory devices include a volatile memory and anon-volatile memory that is applicable for long term data storage. Forexample, the non-volatile memory includes the non-volatile memoryincludes an eFuse, an electrically-erasable programmable read-onlymemory (EEPROM), a flash memory, or a magneto resistive random-accessmemory (MRAM). A robust reference scheme is required to adequately readdata stored in memory cells of the non-volatile memory.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram of a device, in accordance with variousembodiments of the present disclosure;

FIG. 2 is a flow chart of a method illustrating operations of theelectronic device in FIG. 1, in accordance with various embodiments ofthe present disclosure;

FIG. 3A is a schematic diagram of the reference storage unit in FIG. 1having the logic high state, in accordance with various embodiments ofthe present disclosure;

FIG. 3B is a schematic diagram of the reference storage unit in FIG. 1having the logic low state, in accordance with various embodiments ofthe present disclosure;

FIG. 4 is a schematic diagram of the reference circuit in FIG. 1, inaccordance with some other embodiments of the present disclosure;

FIG. 5 is a schematic diagram of the reference circuit in FIG. 1, inaccordance with some other embodiments of the present disclosure;

FIG. 6 is a schematic diagram of the reference circuit in FIG. 1, inaccordance with still other embodiments of the present disclosure;

FIG. 7 is a schematic diagram of the reference circuit in FIG. 6, inaccordance with various embodiments of the present disclosure; and

FIG. 8 is a schematic diagram of the reference circuit in FIG. 6, inaccordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

The terms used in this specification generally have their ordinarymeanings in the art and in the specific context where each term is used.The use of examples in this specification, including examples of anyterms discussed herein, is illustrative only, and in no way limits thescope and meaning of the disclosure or of any exemplified term.Likewise, the present disclosure is not limited to various embodimentsgiven in this specification.

Although the terms “first,” “second,” etc., may be used herein todescribe various elements, these elements should not be limited by theseterms. These terms are used to distinguish one element from another. Forexample, a first element could be termed a second element, and,similarly, a second element could be termed a first element, withoutdeparting from the scope of the embodiments. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

FIG. 1 is a schematic diagram of an electronic device 100 in accordancewith various embodiment of the present disclosure.

As illustratively shown in FIG. 1, the electronic device 100 includes amemory array 110, a reference circuit 120, a sensing unit 130, and aselection circuit 140. The memory array 110 includes memory columns 111,bit lines BL[1]-BL[m], word lines WL[1]-WL[n], and data linesDL[1]-DL[m], in which n and m are positive integers.

For illustration, the memory columns 111 are disposed in parallel witheach other. Each memory column 111 includes n memory cells 112. Each nmemory cells 112 include a switch SW and a storage unit 112A. The switchSW is coupled to a corresponding one of the word lines WL[1]-WL[n] and acorresponding one of the bit lines BL[1]-BL[m]. The storage unit 112A iscoupled between the switch SW and a corresponding one of the data linesDL[1]-DL[m]. Each of the storage units 112A is configured to store bitdata.

The reference circuit 120 is disposed at a side of the memory array 110.The reference circuit 120 includes reference switches RSW, a referencestorage unit 122, a reference storage unit 123, reference bit linesRBL[1]-RBL[2], and reference data lines RDL[1]-RDL[2]. The referenceswitches RSW are disposed in rows and columns. For illustration, thereference switches RSW are arranged in two columns 121A and 121B. Firstterminals of the reference switches RSW in the column 121A are coupledto the reference bit line RBL[1], second terminals of the referenceswitches RSW in the column 121A are coupled to the reference data lineRDL[1], and control terminals of the reference switches RSW in thecolumn 121A are coupled to the word lines WL[1]-WL[n], respectively. Thereference storage unit 122 is coupled between the reference data lineRDL[1] and the sensing unit 130, and configured to store bit data havinga logic high state. Accordingly, when one of the reference switches RSWin the column 121A is turned on, the reference storage unit 122 is thenbiased to transmit the signal I1 having the logic high state accordingto the stored bit data. First terminals of the reference switches RSW inthe column 121B are coupled to the reference bit line RBL[2], secondterminals of the reference switches RSW in the column 121B are coupledto the reference data line RDL[2], and control terminals of thereference switches RSW in the column 121B are coupled to the word linesWL[1]-WL[n], respectively. The reference storage unit 123 is coupledbetween the reference data line RDL[2] and the sensing unit 130, andconfigured to store bit data having a logic low state. Accordingly, whenone of the reference switches RSW in the column 121B is turned on, thereference storage unit 123 is then biased to generated signal I2 havingthe logic low state according to the stored bit data.

In some embodiments, the storage units 112A, the reference storage unit122 and the reference storage unit 123 are implemented with non-volatilememory devices. In further embodiments, the non-volatile memory devicesinclude resistive random-access memory (RRAM) device. The resistance ofthe RRAM device is able to be adjusted to present the bit data havingthe logic high state or the logic low state. In some other embodiments,the non-volatile memory devices include magnetic tunnel junction (MTJ)devices. The magneto resistance of the MTJ device is able to be adjustedto present the bit data having the logic high state or the logic lowstate.

The implementations of the storage units 112A, the reference storageunit 122 and the reference storage unit 123 are given for illustrativepurposes only. Various implementations of the storage units 112A, thereference storage unit 122 and the reference storage unit 123 are withinthe contemplated scope of the present disclosure.

In some embodiments illustrated in FIG. 1, during a read operation, acorresponding one of the word lines WL[1]-WL[n] is activated.Accordingly, two reference switches RSW in the columns 121A and 121B,which are coupled to the activated one of the word lines WL[1]-WL[n],are turned on. The reference storage unit 122 then generates the signalI1 to the sensing unit 130, and the reference storage unit 123 thengenerates the signal I2 to the sensing unit 130. As a result, thesensing unit 130 is able to determine a logic state of the bit data ofthe selected one of then memory cells 112 according to the signals I1and I2. The detailed operations are described below with reference toFIG. 2.

Furthermore, the selection circuit 140 includes switches SEL[1]-SEL[m].First terminals of the switches SEL[1]-SEL[m] are coupled to the datalines DL[1]-DL[m], respectively, second terminals of the switchesSEL[1]-SEL[m] are coupled to the sensing unit 130, and control terminalsof the switches SEL[1]-SEL[m] are configured to receive selectionsignals VSE[1]-VSE[m]. During the read operation, one of the switchesSEL[1]-SEL[m] is turned on, and one of the word lines WL[1]-WL[n] isactivated. Accordingly, the switch SW, which is coupled to the activatedone of the word lines WL[1]-WL[n], are turned on by the correspondingone of the selection signals VSE[1]-VSE[m]. A current ICELL, indicatingthe bit data of the selected one of then memory cells 112, is thentransmitted to the sensing unit 130. Accordingly, the bit data of theselected memory cell 112 is able to be determined by the sensing unit130.

The sensing unit 130 is coupled to the memory array 110 and thereference circuit 120. The sensing unit 130 is configured to determinethe logic state of the bit data of the selected memory cell 112according to the signals I1 and I2. For illustration, in someembodiments illustrated in FIG. 1, the sensing unit 130 includes anaverage current circuit 131 and a sense amplifier 132. Input terminalsof the average current circuit 131 are coupled to the reference storageunits 122 and 123 to receive the signals I1 and I2. A first inputterminal of the sense amplifier 132 is coupled to an output terminal ofthe average current circuit 131 to receive a reference signal IREF. Asecond input terminal of the sense amplifier 132 is coupled to theswitches SEL[1]-SEL[m] to receive the current ICELL. The average currentcircuit 131 is configured to average the signals I1 and I2 to generatethe reference signal IREF. The sense amplifier 132 is configured tocompare the reference signal IREF with the current ICELL, in order todetermine the logic state of the bit data. In some embodiments, theaverage current circuit 131 is implemented with various types of currentmirror circuit.

FIG. 2 is a flow chart of a method 200 illustrating operations of theelectronic device 100 in FIG. 1, in accordance with various embodimentsof the present disclosure. For illustration, the operations of thedevice 100 in FIG. 1 are described by the method 200 with reference toFIG. 2. In some embodiments, the method 200 includes operationsS210-S260.

In operation S210, during a read operation, one of the word linesWL[1]-WL[n] is activated, and a corresponding one of the switchesSEL[1]-SEL[m] is turned on, in order to select a corresponding one ofthe memory cells 112.

In operation S220, the current ICELL, indicating the bit data of theselected memory cell 112, is transmitted from a corresponding one of thedata lines DL[1]-DL[m] to the sense amplifier 132.

For illustration, as illustrated in FIG. 1, during the read operation,the first word line WL[1] is activated, the switch SEL[1] is turned onby the selection signal VSE[ ], and the other switches SEL[2]-SEL[m] areturned off by the selection signals VSE[2]-VSE[m]. Accordingly, thememory cell 112 (hereinafter the selected memory cell 1121) coupled tothe word line WL[1] and the data line DL[1] is selected. The switch SWof the selected memory cell 1121 is then turned on to bias the storageunit 112A of the selected memory cell 1121. Thus, the current ICELL,which is able to indicate the bit data stored in the storage unit 112A,is transmitted from the storage unit 112A to the sense amplifier 132 viathe data line DL[1] and the switch SEL[1].

With continued reference to FIG. 2, in operation S230, a correspondingone of the switches RSW in the column 121A is turned on to generate thesignal I1 to the average current circuit 131. In operation S240, acorresponding one of the switches RSW in the column 121B is turned on togenerate the signal I2 to the average current circuit 131. In operationS250, the average current circuit 131 averages the sum of the signal I1and the signal I2 to generate the reference signal IREF to the senseamplifier 132. In operation S260, the sense amplifier 132 compares thecurrent ICELL with the reference signal IREF, to determine the logicstate of the bit data of the selected memory cell 1121.

For illustration in FIG. 1, when the word line WL[1] is activated, thereference switches RSW in the columns 121A and 121B, which are coupledto the word line WL[1], are turned on. Accordingly, the referencestorage units 122 and 123 are biased by the turn-on reference switchesRSW, to generate the signals I1 and I2 to the average current circuit131. The average current circuit 131 then averages the signals I1 andI2, to generate the reference signal IREF to the sense amplifier 132. Inother words, the level of the reference signal IREF is about half of asum of the signals I1 and I2. The sense amplifier 132 then compares thecurrent ICELL with the reference signal IREF, to determine the logicstate of the bit data of the selected memory cell 1121. For example,when the current ICELL is higher than the reference signal IREF, the bitdata of the selected memory cell 1121 is determined to have the logichigh state. Alternatively, when the current ICELL is lower than thereference signal IREF, the bit data of the selected memory cell 1121 isdetermined to have the logic low state. Effectively, the bit data of theselected memory cell 1121 is read by the electronic device 100.

The above description includes exemplary operations, but the operationsare not necessarily performed in the order described. The order of theoperations disclosed in the present disclosure are able to be changed,or the operations are able to be executed simultaneously or partiallysimultaneously as appropriate, in accordance with the spirit and scopeof various embodiments of the present disclosure.

In some embodiments, the reference switches RSW and the switch SW in then memory cells 112 are configured to have a same feature size. Thus,process/voltage/temperature variations on the memory array 110 aresimilar to those on the reference circuit 120, and accordingly, thereference circuit 120 is able to be utilized to detectprocess/voltage/temperature variations on the memory array 110. Forillustration, with the arrangements of the switches RSW in FIG. 1, thereference circuit 120 is able to track the variations of the wireloading of the memory array 110, for example, including the bit linesBL[1]-BL [m], the switches SW coupled to the bit lines BL[1]-B[m], datalines DL[1]-D L [m], etc. Thus, the reference signal IREF is able to begenerated with the similar variations on the memory array 110.

Compared to some approaches using an external fixed reference signal, amore accurate reference signal IREF is generated by the referencecircuit 120, as illustrated in the embodiments of FIG. 1.

Moreover, in some other approaches, a reference circuit employs the samearchitecture of the memory array 110. In such approaches, the bit datastored in reference storage units of the reference circuit are variedwith each other due to various variations between the reference storageunits. As a result, the reference signal generated by the referencecircuit in such approaches is inaccurate.

Compared with the approaches described above, as illustrated in FIG. 1,the reference switches RSW in the column 121A are coupled to the singlereference storage unit 122, and the reference switches RSW in the column121B are coupled to the single reference storage unit 123. Effectively,the variations between the storage units in the reference circuit 120are minimized. As a result, a more accurate reference signal IREF isable to be generated, compared with the aforementioned approaches.

Reference is now made to FIG. 3A. FIG. 3A is a schematic diagram of thereference storage unit 122 in FIG. 1 having the logic high state, inaccordance with various embodiments of the present disclosure.

As described above, in some embodiments, the reference storage units 122and 123 are implemented with the MTJ devices. In some embodiments, theMTJ device includes a free layer and a pinned layer. As illustrativelyshown in FIG. 3A, the reference storage unit 122 includes a free layer122A and a pinned layer 123B. The free layer 122A of the referencestorage unit 122 is coupled to a first terminal of the reference storageunit 122, and the pinned layer 122B is coupled to a second terminal ofthe reference storage unit 122. In some embodiments, the referencestorage unit 122 is configured to receive a current IT1 flowing from itsfirst terminal, i.e., the free layer 122A, to its second terminal, i.e.,the pinned layer 122B. Accordingly, as shown in FIG. 3A, the magnetmoment of the free layer 122A is anti-parallel to the magnet moment ofthe pinned layer 122B. Under this condition, the reference storage unit122 is configured to have a high magneto resistance. Effectively, thereference storage unit 122 is programmed to have the bit data having thelogic high state.

FIG. 3B is a schematic diagram of the reference storage unit 123 in FIG.1 having the logic low state, in accordance with various embodiments ofthe present disclosure. Corresponding to the reference storage unit 122,as illustrated in some embodiments in FIG. 3B, the reference storageunit 123 includes a free layer 123A and a pinned layer 123B. The freelayer 123A is coupled to the first terminal of the reference storageunit 123. The pinned layer 123B is coupled to the second terminal of thereference storage unit 123. In some embodiments, the reference storageunit 123 is configured to receive a current IT2 flowing from its secondterminal, i.e., the pinned layer 123B, to its second terminal, i.e., thefree layer 123A. Accordingly, as shown in FIG. 3B, the magnet moment ofthe free layer 123A is parallel to the magnet moment of the pinned layer123B. Under this condition, the reference storage unit 123 is configuredto have a low magneto resistance. Effectively, the reference storageunit 123 is programmed to have the bit data having the logic low state.

With continued reference to both of FIG. 1, FIG. 3A, and FIG. 3B, in theembodiments illustrated in FIG. 1, the first terminal, i.e., the freelayer 122A, of the reference storage unit 122 is coupled to thereference data line RDL[1], and the second terminal, i.e., the pinnedlayer 122B, of the reference storage unit 122 is coupled to the averagecurrent circuit 131. Furthermore, the first terminal, i.e., the freelayer 123A, of the reference storage unit 123 is coupled to thereference data line RDL[2], and the second terminal, i.e., the pinnedlayer 123B, of the reference storage unit 123 is coupled to the averagecurrent circuit 131.

FIG. 4 is a schematic diagram of the reference circuit 120 in FIG. 1, inaccordance with some other embodiments of the present disclosure. Withrespect to the embodiment of FIG. 1, like elements in FIG. 4 aredesignated with the same reference numbers for ease of understanding.Alternatively, in the embodiments illustrated in FIG. 4, the secondterminal, i.e., the pinned layer 123B, of the reference storage unit 123is coupled to the reference data line RDL[2], and the first terminal,i.e., the free layer 123A, of the reference storage unit 123 is coupledto the average current circuit 131. In some embodiments, the arrangementof the reference storage unit 123 in FIG. 4 is achieved in a differentlayout design.

As illustratively shown in FIG. 4, the current, for the read operation,flows from the pinned layer 123B to the free layer 123A. As describedabove in FIG. 3B, the current IT2, for the programming operation of thereference storage unit 123, also flows from the pinned layer 123B to thefree layer 123A. In other words, in the embodiments illustrated in FIG.4, the direction of the current for the read operation is the same asthe direction of the current for the programming operation. Accordingly,the operational reliability is able to be further improved, comparedwith the embodiments illustrated in FIG. 1.

FIG. 5 is a schematic diagram of the reference circuit 120 in FIG. 1, inaccordance with some other embodiments of the present disclosure. Withrespect to the embodiment of FIG. 1, like elements in FIG. 5 aredesignated with the same reference numbers for ease of understanding.

Compared with the reference circuit 120 in FIG. 1, in some embodimentsillustrated in FIG. 5, the second terminal, i.e., the pinned layer 123B,of the reference storage unit 123 is coupled to the reference bit lineRBL[2], and the first terminal, i.e., the free layer 123A, of thereference storage unit 123 is coupled to the second terminals of thereference switches RSW in the column 121B. The first terminals of thereference switches RSW in the column 121B are coupled to the referencedata line RDL[2]. With such arrangements, the direction of the currentfor the read operation is the same as the direction of the current forthe programming operation of the reference storage unit 123. As aresult, the operational reliability of the electronic device 100 isfurther improved.

Reference is now made to FIG. 6. FIG. 6 is a schematic diagram of thereference circuit 120 in FIG. 1, in accordance with still otherembodiments of the present disclosure. With respect to the embodiment ofFIG. 1, like elements in FIG. 6 are designated with the same referencenumbers for ease of understanding.

Compared with the reference circuit 120 in FIG. 1, in some embodimentsillustrated in FIG. 6, the reference circuit 120 further includes areference word line RWL, and the reference circuit 120 only utilizes tworeference switches RSW1 and RSW2. For illustration, a first terminal ofthe reference switch RSW1 is coupled to the reference bit line RBL[1], asecond terminal of the reference switch RSW1 is coupled to the firstterminal of the reference storage unit 122, and a control terminal ofthe reference switch RSW1 is coupled to the reference word line RWL. Afirst terminal of the reference switch RSW2 is coupled to the referencebit line RBL[2], a second terminal of the reference switch RSW2 iscoupled to the first terminal of the reference storage unit 123, and acontrol terminal of the reference switch RSW2 is coupled to thereference word line RWL. Second terminals of the reference switches areconfigured to transmit the signals I1 and I2 to the average currentcircuit 131.

In some embodiments, during the read operation, the reference word lineRWL and one of the word lines WL[1]-WL[n] are activated at the sametime, in order to transmit the current ICELL and the signals I1 and I2.Alternatively, in some other embodiments, the reference word line RWL iskept being activated. The operations of the reference circuit 120 inFIG. 6 are similar with the operations illustrated in FIG. 2, and therepetitious descriptions are thus not given here.

The configurations of the reference word line RWL is given forillustrative purposes only. Various configurations of the reference wordline RWL are within the contemplated scoped of the present disclosure.

Compared with some approaches employing the same architecture of thememory array as the reference circuit, as discussed above, in theembodiments illustrated in FIG. 6, the variations between the referencestorage units in the reference circuit 120 are minimized. Accordingly, amore accurate reference signal IREF is able to be generated.

Reference is now made to both of FIG. 3B and FIG. 7. FIG. 7 is aschematic diagram of the reference circuit 120 in FIG. 6, in accordancewith various embodiments of the present disclosure. With respect to theembodiment of FIG. 1, like elements in FIG. 7 are designated with thesame reference numbers for ease of understanding.

As illustrated in FIG. 3B, the reference storage unit 123 is able to beimplemented with the MTJ device. Compared with the reference circuit 120in FIG. 6, in some embodiments illustrated in FIG. 7, the secondterminal, i.e. the pinned layer 123B in FIG. 3B, of the referencestorage unit 123 is coupled to the second terminal of the referenceswitch RSW2, and the first terminal, i.e., the free layer 123A in FIG.3B, of the reference storage unit 123 is coupled to the average currentcircuit 131. As described above, with such arrangements, the directionof the current for the read operation is the same as the direction ofthe current for the programming operation of the reference storage unit123. As a result, the operational reliability of the electronic device100 is further improved.

Reference is now made to both of FIG. 3B and FIG. 8. FIG. 8 is aschematic diagram of the reference circuit 120 in FIG. 6, in accordancewith various embodiments of the present disclosure. With respect to theembodiment of FIG. 1, like elements in FIG. 8 are designated with thesame reference numbers for ease of understanding.

Compared with the reference circuit 120 in FIG. 6, in some embodimentsillustrated in FIG. 8, the second terminal, i.e., the pinned layer 123B,of the reference storage unit 123 is coupled to the reference bit lineRBL[2], and the first terminal, i.e., the free layer 123A, of thereference storage unit 123 is coupled to the second terminal of thereference switch RSW2. The first terminal of the reference switch RSW2is coupled to the reference data line RDL[2]. With such arrangements,the direction of the current for the read operation is the same as thedirection of the current for the programming operation of the referencestorage unit 123. As a result, the operational reliability of theelectronic device 100 is improved.

As described above, the device 100 in the present disclosure is able togenerate a reference signal to be compared with the bit data. Moreover,with the arrangements of the reference circuit illustrated in variousembodiments, a more accurate reference signal is generated. Accordingly,the operational reliability of the memory device is able to be improved.

In this document, the term “coupled” may also be termed as “electricallycoupled,” and the term “connected” may be termed as “electricallyconnected”. “Coupled” and “connected” may also be used to indicate thattwo or more elements cooperate or interact with each other.

In some embodiments, a device is disclosed that includes memory cells, afirst reference switch, a second reference switch, a first referencestorage unit, a second reference storage unit, and an average currentcircuit. The memory cells are each configured to store corresponding bitdata. The first reference switch and the second reference switch areturned on when a word line is activated. The first reference storageunit generates a first signal having a first logic state when the firstreference switch is turned on. The second reference storage unitgenerates a second signal having a second logic state when the secondreference switch is turned on. The average current circuit averages thefirst signal and the second signal to generate a reference signal to becompared with a current indicating the bit data of one memory cell, inorder to determine a logic state of the bit data of the memory cell.

Also disclosed is a method that includes operations below. A firstsignal having a first logic state is generated by a first referencestorage unit according to bit data of a corresponding memory cell ofmemory cells, and the first signal is transmitted through a firstreference switch when a word line is activated, to an average currentcircuit. A second signal having a second logic state is generated by asecond reference storage unit when the word line is activated. The firstsignal and the second signal are averaged by the average currentcircuit, to generate a reference signal. The reference signal iscompared with a current indicating the bit data of the correspondingmemory cell, by a sense amplifier, to determine the logic state of thebit data.

Also disclosed is a device that includes memory cells, referenceswitches, reference storage units, and an average current circuit. Thememory cells are coupled to a data line, wherein each of the memorycells is configured to store bit data. The reference storage units areconfigured to be biased by the p reference switches to generate at leasta first signal and a second signal, and the first signal and the secondsignal have logic states that are different from each other. The averagecurrent circuit is configured to generate a reference signal byaveraging a sum of the first signal and the second signal, to becompared with a current indicating corresponding bit data of acorresponding memory cell in the memory cells.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device, comprising: a plurality of memory cellseach configured to store corresponding bit data; a first referenceswitch and a second reference switch that are configured to be turned onwhen a word line is activated; a first reference storage unit configuredto generate a first signal having a first logic state when the firstreference switch is turned on; a second reference storage unitconfigured to generate a second signal having a second logic state whenthe second reference switch is turned on; and an average current circuitconfigured to average the first signal and the second signal to generatea reference signal to be compared with a current indicating thecorresponding bit data of a corresponding memory cell in the pluralityof memory cells, in order to determine a logic state of thecorresponding bit data of the corresponding memory cell, wherein thefirst reference storage unit is coupled between the first referenceswitch and the average current circuit and is configured to receive thecorresponding bit data through the first reference switch.
 2. The deviceof claim 1, wherein the first reference switch is coupled between afirst reference bit line and the first reference storage unit, and thesecond reference switch is coupled between a second reference bit lineand the second reference storage unit.
 3. The device of claim 2, whereineach of the first reference storage unit and the second referencestorage unit comprises a first terminal and a second terminal, the firstreference storage unit is configured to receive a current flowing fromthe first terminal to the second terminal, to store bit data having thefirst logic state, and the second reference storage unit is configuredto receive a current flowing from the second terminal to the firstterminal, to store bit data having the second logic state, wherein thecurrent received by the first reference storage unit is different fromeach one of the first signal and the second signal, and the currentreceived by the second reference storage unit is different from each oneof the first signal and the second signal.
 4. The device of claim 3,wherein the first terminal of the first reference storage unit iscoupled to the first reference switch, and the second terminal of thefirst reference storage unit is configured to generate the first signal,wherein the first terminal of the second reference storage unit iscoupled to the second reference switch, and the second terminal of thesecond reference storage unit is configured to generate the secondsignal.
 5. The device of claim 3, wherein the first terminal of thefirst reference storage unit is coupled to the first reference switch,and the second terminal of the first reference storage unit isconfigured to generate the first signal, wherein the second terminal ofthe second reference storage unit is coupled to the second referenceswitch and the first terminal of the second reference storage unit isconfigured to generate the second signal.
 6. The device of claim 3,wherein a first terminal of the first reference switch is coupled to thefirst reference bit line, a second terminal of the first referenceswitch is coupled to the first terminal of the first reference storageunit, a control terminal of the first reference switch is coupled to areference word line, and the second terminal of the first referencestorage unit is configured to output the first signal, wherein a firstterminal of the second reference switch is configured to output thesecond signal, a second terminal of the second reference switch iscoupled to the first terminal of the second reference storage unit, acontrol terminal of the second reference switch is coupled to thereference word line, and the second terminal of the second referencestorage unit is coupled to the second reference bit line.
 7. The deviceof claim 1, further comprising: a sense amplifier configured todetermine the logic state of the corresponding bit data of thecorresponding memory cell according to the reference signal.
 8. A methodcomprising: receiving, by a first reference storage unit through a firstreference switch, bit data of a corresponding memory cell of memorycells; generating, by the first reference storage unit coupled betweenthe first reference switch and an average current circuit, a firstsignal having a first logic state according to the bit data of thecorresponding memory cell of the memory cells, and transmitting thefirst signal through the first reference switch when a word line isactivated, to the average current circuit; generating, by a secondreference storage unit coupled between a second reference switch and theaverage current circuit, a second signal having a second logic statewhen the word line is activated; averaging the first signal and thesecond signal, by the average current circuit, to generate a referencesignal; and comparing the reference signal with a current indicating thebit data of the corresponding memory cell, by a sense amplifier, todetermine a logic state of the bit data.
 9. The method of claim 8,wherein the generating the first signal comprises: turning on the firstreference switch when the word line is activated, wherein the firstreference switch is coupled to the average current circuit via the firstreference storage unit and is coupled to the word line, and the wordline is coupled to the corresponding memory cell; and biasing the firstreference storage unit, by the first reference switch, to generate thefirst signal.
 10. The method of claim 8, wherein the generating thefirst signal comprises: turning on the first reference switch when theword line is activated, wherein the first reference switch is coupled tothe word line, and the word line is a reference word line that isdifferent from word lines that are coupled to the memory cells; andbiasing the first reference storage unit, by the first reference switch,to generate the first signal.
 11. The method of claim 8, furthercomprising: turning on a switch that is coupled between thecorresponding memory cell and the sense amplifier, to transmit thecurrent indicating the bit data of the corresponding memory cell to thesense amplifier.
 12. The method of claim 11, wherein the switch isturned on in response to a selection signal during a read operation. 13.A device, comprising: a plurality of memory cells coupled to a dataline, wherein each of the memory cells is configured to store bit data;a plurality of reference switches; a plurality of reference storageunits configured to be biased by the plurality of reference switches andconfigured to receive, through the plurality of reference switches, thebit data to generate at least a first signal and a second signal, andthe first signal and the second signal have logic states that aredifferent from each other; and an average current circuit configured togenerate a reference signal by averaging a sum of the first signal andthe second signal, to be compared with a current indicatingcorresponding bit data of a corresponding memory cell in the pluralityof memory cells.
 14. The device of claim 13, wherein the plurality ofreference switches comprise: a first reference switch coupled to areference word line; and a second reference switch coupled to thereference word line.
 15. The device of claim 14, wherein the pluralityof reference storage units comprise: a first reference storage unitconfigured to be biased to generate the first signal when the firstreference switch is turned on; and a second reference storage unitconfigured to be biased to generate the second signal when the secondreference switch is turned on.
 16. The device of claim 15, wherein eachof the plurality of reference storage units comprises a first terminaland a second terminal, each of the plurality of reference storage unitsis configured to receive a current flowing from the first terminal tothe second terminal, to store first bit data, and configured to receivea current flowing from the second terminal to the first terminal, tostore second bit data, wherein the first bit data and the second bitdata have logic states that are different from each other.
 17. Thedevice of claim 16, wherein the first terminal of the first referencestorage unit is coupled to the first reference switch, and the secondterminal of the first reference storage unit is configured to generatethe first signal, wherein the first terminal of the second referencestorage unit is coupled to the second reference switch, and the secondterminal of the second reference storage unit is configured to generatethe second signal.
 18. The device of claim 16, wherein the firstterminal of the first reference storage unit is coupled to the firstreference switch, and the second terminal of the first reference storageunit is configured to generate the first signal, wherein the secondterminal of the second reference storage unit is coupled to the secondreference switch, and the first terminal of the second reference storageunit is configured to generate the second signal.
 19. The device ofclaim 16, wherein a first terminal of the first reference switch iscoupled to a first reference bit line, a second terminal of the firstreference switch is coupled to the first terminal of the first referencestorage unit, a control terminal of the first reference switch iscoupled to the reference word line, and the second terminal of the firstreference storage unit is configured to output the first signal, whereina first terminal of the second reference switch is configured to outputthe second signal, a second terminal of the second reference switch iscoupled to the first terminal of the second reference storage unit, acontrol terminal of the second reference switch is coupled to thereference word line, and the second terminal of the second referencestorage unit is coupled to a second reference bit line.
 20. The deviceof claim 13, wherein a number of the plurality of reference switches isthe same as a number of the plurality of reference storage units.